Many portable digital devices have a wireless network interface, such as a Wi-Fi compatible interface, for data communications. In addition, in support of portability, many of these devices are also configured to operate using battery power. Often, however, such devices have power management mechanisms that place the wireless network interface in a so-called sleep mode when external communications through the interface are not required. Through the use of the sleep mode, power consumption can be reduced, thus improving battery life.
However, because the wireless network interface is in the sleep mode, the device cannot receive any communications (e.g., a push notification) through the wireless network interface. For example, when a Wi-Fi interface of a tablet computer is in the sleep mode, and is therefore inactive, an instant messenger application on the device cannot receive, through the Wi-Fi interface, a notification requesting a chatting session from an instant messaging server. The use of the sleep mode, while perhaps extending battery life, can limit, in some circumstances, the greatest possible use of the device.
Some devices have alternate communication mechanisms which do not suffer from the above problem. For example, in the context of 2G/3G/4G mobile network-equipped devices, it is known to provide a service where a persistent communication channel is maintained between the device and a messaging server. Notification messages from external services can be therefore delivered to the device over the persistent communication channel. However, in Wi-Fi only devices, such as ebook readers and tablet computers, this alternate mechanism (persistent communication channel) is unavailable and therefore such devices can miss important notifications when the device's Wi-Fi interface has been deactivated in order to save battery power.